1. Field of the Invention
The present invention relates to a photolithographic process, and more particularly, to a method of removing photoresist and a photoresist rework method.
2. Description of the Related Art
Photoresist is an indispensable material for a photolithographic process and is also one of the most critical factors in semiconductor technology. In a photolithographic process, a pattern on a mask is transferred to a photoresist layer which has different dissolution rates to a chemical solution before and after an exposure process. The mask formed by the photoresist should be removed after a subsequent process, such as a dry etch process, a wet etch process, or an ion implantation process is performed. Accordingly, the following process after the removal process will not be affected. Thus, how to fast clean photoresist without leaving residue and to reduce the manufacturing costs has become an essential research topic in the semiconductor industry.
For the time being, the method of removing photoresist comprises the dry photoresist removal method by using plasma to strip photoresist. In this method, oxygen plasma reacts with photoresist to generate carbon monoxide, carbon dioxide and water; then they are pumped out by a vacuum system. The dry photoresist removal method has been widely applied to the present process. In order to completely remove photoresist, a wet photoresist removal method may further be carried out after the dry photoresist removal method to remove ash and other particles left by the plasma reaction. Traditionally, the wet photoresist removal method uses organic solution to destroy the structure of the photoresist so that the photoresist dissolves in the organic solution and is removed.
Most of the traditional photoresist removal methods are performed in areas that are separate from the general photolithography area. The photoresist removal step cannot be immediately performed in such process as wafers should be transferred to the photoresist-removal area for processing. The process to perform these steps in different areas is troublesome and affects the manufacturing throughput.
In another aspect, if defects are found before the photolithographic processes such as photoresist coating, exposure, baking or development, ultraviolet curing or plasma bombardment, rework is required to remove photoresist in order to avoid any impacts of the subsequent processes. However, the present semiconductor process requires transferring the defective wafers to the photoresist-removal areas for reworking process before the photoresist removal process is performed. Since the rework can not be directly carried out in a manufacturing process, the method is very time consuming and costly.